Recently, along with the trend toward high speed of semiconductor devices and miniaturization of wiring patterns, Cu having higher conductivity than Al and also having high electromigration resistance has been in the spotlight as a material for the wiring. Conventionally, a Cu wiring has been formed by electroplating, and Cu has been used as a seed of the Cu wiring. However, in view of better embedding characteristic, studies have been made to use Co instead of Cu as the seed of the Cu wiring formed by electroplating. Further, it also has been proposed to use a Co film as a Cu diffusion barrier layer.
As for a Co film forming method, a physical vapor deposition (PVD) method represented by sputtering has been widely employed. However, it is disadvantageous in that step coverage deteriorates due to miniaturization of semiconductor devices.
Therefore, there is provided a chemical vapor deposition (CVD) method for forming a Co film on a substrate by thermal decomposition of a film forming material gas containing Co or reduction reaction using a reduction gas of the film forming material gas. The Co film formed by the CVD method has a high step coverage and can be easily formed in a thin, long and deep pattern. Therefore, the Co film has high conformability to a fine pattern and is preferably used as a Cu plating seed layer.
As for a Co film forming method by a CVD method, there is suggested a method for supplying gaseous cobalt carbonyl (Co2(CO)8) as a film forming material into a chamber and thermally decomposing the cobalt carbonyl on a substrate in the chamber (e.g., Journal of The Electrochemical Society, 146(7)2720-2724(1999)).
However, when Co2(CO)8 is used as a film forming material, Co4(CO)12 may be generated by polymerization reaction during the transfer of Co2(CO)8 and, thus, the mixture of Co2(CO)8 and Co4(CO)12 may be supplied. If the film forming material supplied in such mixed state is decomposed on the substrate, a Co film having poor step coverage is formed and the reproducibility of the film formation process deteriorates.